#include <string.h>

char * strstr( const char * str1, const char * str2 ) {
  const char * cp = str1;
  const char * s1;
  const char * s2;
  if( !*str2 )
  { return str1; }
  while( *cp ) {
    s1 = cp;
    s2 = str2;
    while( *s1 && *s2 && !( *s1 - *s2 ) )
    { s1++, s2++; }
    if( !*s2 )
    { return( ( char* )cp ); }
    cp++;
  }
  return ( NULL ) ;
}
